Flask No. I Manganese oxide, black, = 150 m.g.
N/10 nitric acid = 14.93 c.c.
[= Mn in KMnO₄ in No. II or No. III]
Water = 27.46 c.c.
[Total solution = 42.39 c.c.]
Flask No. II Potassium permanganate = 20 c.c. = 117.71 m.g.
N/10 nitric acid = 22.39 c.c.
[= K and Mn in KMnO₄]
[Total solution = 42.39 c.c.]
Flask No. III Potassium permanganate = 20 c.c. = 117.71 m.g.
N/10 nitric acid = 22.39 c.c.
[= K and Mn in KMnO₄]
Manganese oxide, black = 150 m.g.
[Total solution = 42.39 c.c.]
The first two results are from experiments in which the action was
stopped at the first loss of the color of potassium permanganate.
The last two are the results from experiments in which the action
was stopped after the oxide had settled leaving a clear colorless
supernatant liquid. The amount of oxygen given off in any one case is
expressed in the table as the number of atoms of oxygen derived from
each molecule of potassium permanganate, as follows:
A = N/10 nitric acid. No. of molecules.
------------------+-------------------------+--------------------
Flask I | Flask II | Flask III
------------------+-------------------------+--------------------
Black | Potassium | Potassium
oxide A |permanganate A | permanganate A
150 m.g. | 20 c.c. = | 20 c.c.
| 117.71 m.g. | = 117.71 m.g.
----------------------+-------------------------+----------------
1 2 hours.
0.00 2 0.18 3 1.337 3
2 2¼ hours
0.02 ” 0.24 ” 1.335 ”
3 2½ hours
0.02 ” 0.44 ” 1.402 ”
4 4½ hours
0.00 ” 0.55 ” 1.362 ”
The volume of the oxygen evolved is considerably smaller than that
obtained when the brown oxide was used. It is nevertheless larger
than could have been evolved if all of the manganese had been left
in the dioxide condition at the close of the experiment. This fact
indicates that there was a slight reduction of the manganese dioxide
after the disappearance of the color of the permanganate. That such a
reduction of manganese dioxide does take place will be made apparent
by a comparison of the results of the first two experiments in which
the oxygen was measured soon after the color of permanganate had
disappeared, with the results of the last two experiments in which the
oxygen was determined after a longer interval. It will be noticed in
this as in the series of experiments with the brown oxide that the rate
of the evolution of oxygen liberated in flask No. II increases with the
time of heating.
The Amount of Nitric Acid neutralized.
A few experiments were made to determine how much nitric acid is
neutralized under the conditions which prevailed in the foregoing
experiments.
I. The flask contained brown oxide 150 m.g. N/10 nitric acid 6.98 c.c.
and was heated for three hours in the water-bath.
Acid neutralized = 4.51 c.c. = 64.60 percent.
II. The flask contained brown oxide 150 m.g. N/10 nitric acid 6.98 c.c.
and was heated for 50 minutes in the water-bath.
Acid neutralized = 3.09 c.c. = 44.20 percent.
III. The flask contained brown oxide 150 m.g. N/10 nitric acid 7.46
c.c. and was heated for fifty minutes in the water-bath.
Acid neutralized = 3.16 c.c. = 42.30 percent.
IV. The flask contained brown oxide 150 m.g. N/10 nitric acid 7.46 c.c.
and was heated for 15 minutes in the water-bath.